EASA has received reports regarding potential loss of ATC transponder transmissions due to a loose connection of an installed resistor in the Gables ATC/TCAS control panel types G7490, G7492, G7493 series. Gables Engineering has contacted known operators to advise them to return the control panels for modification. At this time, EASA has determined that this airworthiness concern is not an unsafe condition that would warrant airworthiness directive (AD) action under Regulation (EC) 1702/2003, Part 21A.3B.